In operation of a concrete pump on a construction site it is necessary to be able to determine the delivered quantity of the concrete substantially immediately and without time delay. In various types of use, the delivery rate is a relevant quantity and must be detected.
For this purpose, it has so far been provided that for example the driver of a construction vehicle with a concrete pump, which in practice constitutes a piston pump, specifies the quantity to be delivered per pump stroke of the concrete pump. On the basis of this specification and of the pump strokes performed, the delivered quantity of the concrete can then be calculated.
However, it turns out to be problematic that the determination of the pump strokes performed cannot easily be effected. This requires a high technical effort, since a detection of the pump strokes for example is effected directly at the pump via limit switches. However, this necessitates e.g. an expensive cable arrangement from the pump to the machine processing the concrete or some other kind of signal transmission e.g. via a radio link. Mounting a limit switch on the different types of pumps, however, is problematic in particular in mobile concrete pumps.
Therefore, it is the object of the present disclosure to develop a method as mentioned above in an advantageous way, in particular to the effect that a safe and simple determination of the delivery rate of the liquid can be achieved.
In accordance with the present disclosure, this object is solved, in one example, by a a method for determining the delivery rate of a liquid conveying device, (e.g., at least one piston pump). On the basis of measured values concerning the pressure of the liquid in the liquid conveying device, the number of the pump strokes of the liquid conveying device is determined, in particular substantially calculated, by series connection of a plurality of filters with adaptive filter length and variable detection limits. The filter may be a digital filter (discrete filter) implemented in a digital electronic controller receiving the measured values, such as via sensors coupled to the piston pump. The determined delivery rate may be outputted and/or used to determine the delivery rate of the liquid conveying device, which can then be communicated and/or displayed via a display device.
In this method it is in particularly advantageous that the time delay is small with regard to the process, i.e., the determination of the delivery rate of a liquid conveying device.
The liquid conveying device in particular can be a concrete pump, wherein this concrete pump can be arranged for example on a construction vehicle or some other mobile base. Such liquid conveying device in particular includes a telescopable or foldable boom on which a concrete delivery hose and/or tube or a combination of a concrete delivery hose and a concrete delivery tube is arranged, by which the liquid concrete can be delivered to the corresponding unloading location on a construction site. By determining measured values concerning the pressure, in particular concerning the delivery pressure, it is possible to advantageously indirectly, but exactly determine the number of the pump strokes of the piston pump serving as liquid conveying device, whereby the quantity of liquid delivered by device of the liquid conveying device thereby can be inferred or calculated. Accordingly, this is an indirect delivery rate measurement of the liquid which is delivered by device of the liquid conveying device.
Possible methods for the analysis of measurement data such as the use of mean value filters for eliminating peaks or for generating auxiliary signals, offset elimination by high-pass filtering, discrete Fourier transformation, offset removal by signal less averaged signal (low pass), time derivation (difference quotient), minima and maxima determination within a rectangular window, envelopes, for example multiplicative increase or reduction, cross-correlation or an adaptive window length for example of the form
  N  =                    N        old            +              N        new              2  are not sufficiently suited as such to solve the object with the given object. In liquid conveying devices, which deliver liquids such as concrete over in part considerably delivery distances, it can occur that the determined measured values concerning the pressure on the whole provide a signal or signal pattern which does not reveal any pressure fluctuations, although concrete definitely is pumped through the liquid conveying device. Only a combination of averaging and adaptive window or filter length and variable detection limits allows an evaluation of the measured values concerning the pressure with sufficient accuracy to the effect that the performed number of pump strokes of the piston pump and hence the delivery rate can be determined.
The calculation of the number of pump strokes and based thereon the determination of the concrete delivery rate with reference to the known or specified delivery rate of the liquid per pump stroke thus is effected easily, accurately and so fast that the determination of the delivery rate of the liquid conveying device substantially is possible without time delay. For example, the calculation is effected by an evaluation and/or calculation device, such as an electronic controller, which for example can be part of the control and/or regulation unit of the liquid conveying device.
It is furthermore conceivable that the determination of the delivery rate is effected independent of the DC component of the measured value and/or with highly noisy and/or disturbed and/or shifted measured values and/or without prior knowledge of and/or reference to the current pump frequency of the liquid conveying device.
Furthermore, it can be provided that at least three filters are provided and/or that the filters are moving-averages filters (MA filters), by which an evaluation of the individual filtered signals is effected and the dominant signal frequency is converted into a square-wave signal, so that the detection of a pump stroke of the liquid conveying device can be effected in the form of a flank detection.
In addition, it is possible that at least one first MA filter is a mean value filter over at least five measured (e.g., digitally sampled) values for eliminating peaks and/or that beside the at least one first MA filter an at least second and an at least third MA filter is provided, wherein the third MA filter is a mean value filter whose filter length is dependent on the pump frequency of the liquid conveying device and the second MA filter is a mean value filter whose filter length is half as long as the third MA filter.
It is furthermore conceivable that when evaluating the measured values at least one mean fade-out time is formed, wherein the limits for the mean fade-out time are dependent on the pump frequency of the liquid conveying device.
In addition, it can be provided that a distance time is provided, which describes the period between two ascending flanks of a square-wave signal, wherein a pressure increase only is detected after 75% of a mean distance time and 95% of the minimum fade-out time and/or that a pressure decrease only is detected after 75% of the mean fade-out time. The aforementioned values are approximate values which serve as reference point for the values to be adjusted.
Furthermore, the present disclosure relates to a liquid conveying device. Accordingly, it is provided that a liquid conveying device is provided with at least one device for determining the delivery rate of the liquid conveying device, wherein on the basis of measured values concerning the pressure of the concrete in the liquid conveying device the number of the pump strokes of the liquid conveying device can be determined by series connection of a plurality of filters with adaptive filter length and variable detection limits, wherein by the liquid conveying device, which in particular includes a corresponding evaluation and/or calculation device, such as an electronic controller, the methods described herein can be carried out.
When carrying out the method by via the liquid conveying device, the liquid conveying device can be designed such that the method substantially can be carried out by the evaluation and/or calculation device of the liquid conveying device.
In particular, the liquid conveying device can have the aforementioned liquid conveying device features described in connection with the method for determining the delivery rate of the liquid conveying device.
In addition, the present disclosure relates to a construction vehicle with at least one liquid conveying device as described herein.
Further details and advantages of the present disclosure will now be explained in detail with reference to an exemplary embodiment illustrated in the drawings.